1. Field of the Invention
Embodiments of the present invention generally relate to electrochemical mechanical polishing. More particularly, embodiments of the present invention relate to a method and apparatus for retaining electrolyte on a rotating platen.
2. Description of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large-scale integration (ULSI) of semiconductor devices. However, as the limits of circuit technology are pushed, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on processing capabilities. Reliable formation of interconnects is important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and dies.
Multilevel interconnects are formed using sequential material deposition and material removal techniques on a substrate surface to form features therein. As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization prior to further processing. Planarization or “polishing” is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing excess deposited material and removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials to provide an even surface for subsequent lithography and processing.
Electrochemical mechanical polishing (ECMP) is one method of planarizing a surface of a substrate. ECMP removes conductive materials from a substrate surface by electrochemical dissolution while polishing the substrate with a reduced mechanical abrasion compared to conventional chemical mechanical planarization (CMP) processes, which may require a high relative down force on a substrate to remove materials, such as copper, from the substrate. A typical ECMP system includes a substrate support and two electrodes disposed within an electrolyte containment basin. In operation, metal atoms on a surface of a substrate are ionized by an electrical current from a source of potential, such as a battery or other voltage source connected to the two electrodes. The metal ions dissolve into the surrounding electrolyte solution at a rate proportional to the electric current. The metal ions from the substrate (anode) plate the electrode (cathode), fall out of the solution as a precipitate of complexes, or remain in the solution. The density of the metal ions depends greatly on the chemistry of the metals and the solution.
ECMP processes require some amount of electrolyte solution to be maintained on a perforated processing pad surface to fill the perforations in order to conduct current between the electrodes. However, the rotational velocity of the pad causes centrifugal acceleration of the electrolyte on the pad surface which biases the electrolyte away from the center of the pad, thereby causing the electrolyte to drain from the pad.
The prior art contains different concepts addressing the draining problem, each having its own disadvantages, for example, a platen gutter which is height restricted by clearance between the polishing head and the platen, a platen cover which adversely affects the polishing process, and a flow directing wiper arm which contacts the pad surface, thereby adversely affecting the polishing process.
Therefore, there exists a need in the art for retaining electrolyte on a polishing pad surface without affecting the polishing process.